The alveoli are lined with mucus and are surrounded by a network of blood capillaries. They have very thin walls for gases to be absorbed through. An individual air sac is called an alveolus. The layer of moisture in the alveoli allows gases to dissolve so that they can diffuse quickly.
<span>a strong downward current of air from a cumulonimbus cloud, usually associated with intense rain or a thunderstorm.</span>
Answer:
the cell membrane is the semi-permeable protective cover that keeps the cell held together. the cytoplasm is semi-fluid within the cell membrane that keeps the cell in shape.
Explanation: